The present invention relates to an engine starter system for supplying an electric current to the starter mechanism for an engine to start the engine
Engines mounted on motor vehicles are usually started by a starter mechanism which comprises a series motor and a magnet switch. Electric power is supplied from a power supply to the starter mechanism to energize the motor to rotate the crankshaft of the engine, thereby starting the engine. If a battery of +12 V, for example, is mounted as the power supply on the motor vehicle, then a large current of 100 A or greater is supplied from the battery to the starter mechanism at the time the engine is started.
There was an attempt to employ loads or accessories on motor vehicles with a unified voltage specification of 12 V while employing a starter circuit with a voltage rating of 24 V for reducing a large current required when starting an engine, to half. Motor vehicles with such a 24 V starter circuit and 12 V accessory circuits required a plurality of 12 V batteries to be used in combination. These combined 12 V batteries could not be charged and discharged in a balanced condition, and required a more troublesome maintenance process and had a shorter service life than a single 12 V or 24 V battery. While the motor vehicles had certain merits such as lower wiring and relay requirements because of the reduced starting current needed, they are not available in the market today owing to the limited battery maintenance and service life.
When the engine on a motor vehicle is started, the starter mechanism consumes a very large current and the battery voltage drops temporarily. Therefore, sufficient electric power cannot be supplied to accessories such as a car radio, a tranceiver, etc., for a few seconds while the starter mechanism is in operation. One solution to this problem is proposed in Japanese Laid-Open Utility Model Publication No. 56(1981)-1466644. The proposed system comprises a series-connected circuit of an engine starter and a starter switch and another series-connected circuit of a unidirectional element and a large-capacity capacitor. These series-connected circuits are connected parallel to the battery. The opposite terminals of the capacitor are connected to accessories on the motor vehicle for supplying electric power from the capacitor to the accessories. The capacitor serves as a power supply for the accessories and is effective to prevent an accessory shutdown at the time of starting the engine. However, when the engine is started, the capacitor is disconnected from the starter circuit by a diode, and hence is not designed for use as a power supply for the starter mechanism.